1. Field of the Invention
The invention is based on an armature shaft for an electrical machine having a plurality of notches, which extend along the circumference of the armature shaft essentially parallel to the longitudinal direction and form a notching heap.
2. Description of the Prior Art
In packet-making by means of notches, two notches each extending longitudinally are made in the armature shaft with a two-piece, U-shaped tool. The notching creates a heap or ridge of displaced material, which increases the outer diameter of the armature shaft in the notched region. As a result, the armature shaft can be firmly press-fitted into the bore in the packet. The notching heap joins each lamination in the packet solidly to the armature shaft. Moreover, because the notching heap slightly penetrates the laminations, a positive engagement is achieved which markedly increases the torques of the packet. The axial displacement force of the packet, however, is usually slight, above all at the end laminations, and these laminations must therefore as a rule also be ring-calked. By means of notches, an extremely stable connection is created, which meets the most stringent demands in terms of the quality of the balancing and low-vibration operation. Thus very low-noise motors can be produced. However, complicated technical production prerequisites must be met, if the method is to be used at all with long, thin shafts.
In production, bore tolerances, for instance, selected must be close. The heaps of the notches must likewise have close tolerances; otherwise, the press-fitting forces exceed the buckling force of the shaft. Because of the close tolerances, introducing the shaft is difficult. A high rejection rate must be expected, because of cold welding of shaft material to the packet sheet metal. Especially long packets, with a length of about 50 mm, for instance, have a particularly pronounced tendency to cold welding because of the long press-fitting distances. Because of the relatively high press-fitting forces, excessively great errors of concentricity often occur at the shaft upon press-fitting and must then be corrected manually or by machine in a further operation. Packet-making by press-fitting a notched shaft is indeed the appropriate method for producing low-noise motors that are relatively impact-resistant. However, they require considerable effort and expense technically. Rejections from buckling of the shaft after seizing are highly likely in the press-fitting process.
Notches with a notching heap are in contrast to knurling, in which no notching heaps are created, or only indentations are created because of compaction of the material. This makes knurling unsuitable for an armature shaft to which an armature packet is to be secured.